(1) Field of the Invention
The invention relates to an optical engine, especially to an optical engine with well reliability and high image contrast.
(2) Description of the Prior Art
Digital light processing (DLP) projector is the projection system developed by Texas Instruments Incorporated (TI), applying mirror reflection imaging principle and owning the advantages of full digital, high contrast and exquisite image. Meanwhile, the projector using this technology is capable of effectively reducing its volume and weight and achieving light, thin, short and small.
Usually, a DLP projector has an optical engine, which takes actions of light beam generation, processing and transmission inside and produces a lot of heat. If the optical engine often has high temperature inside, the reliability and the service life of the inner components may decrease greatly. Therefore, many optical engines adopt heat dissipation design.
Referring to FIG. 1 for the schematic view of a conventional optical engine with heat dissipation device, an optical engine 10 has at least a light source system 11, a housing 12, a digital micromirror device (DMD) 13, a projection lens 14 and a heat dissipation device 16.
The light source system 11 includes a light source, a color filter rotary disc, a focusing lens and etc. for providing an incident light beam 111.
The DMD 13 is disposed in the housing 12 and located in the light path of the incident light beam 111 for receiving the incident light beam 111 from the light source 11, modulating and reflecting the incident light beam 111 to generate an image light beam 112 (ON light) or a dumped light beam 113 (OFF light).
The DMD 13 has many tiny movable lenses for reflecting the incident light beam 111 out. The DMD 13 reflects the above mentioned image light beam 112 or the dumped light beam 113 by controlling deflection angle of each tiny movable lens via digital signal. Each movable lens reflects the image light beam 112 or the dumped light beam 113 with different predetermined angles, so the light paths of the image light beam 112 and the dumped light beam 113 is anticipated.
The projection lens 14 is connected with the housing 12 and located in the light path of the image light beam 112 for projecting the image beam 112 to an outer screen to form an image.
The housing 12 has an opening 15 located in the light path of the dumped light beam 113. The dimension of the opening 15 makes the dumped light beam 113 to reflect into the opening 15 totally. The heat dissipation device 16 is fixed on the housing 12 and covers the opening 15. Thus, the dumped light beam 113 is projected to the heat dissipation device 16, and the heat of the dumped light beam 113 is absorbed and dissipated by the heat dissipation device 16. Besides, a heat insulation device 17 is disposed between the heat dissipation device 16 and the housing 12 to insulate heat conduction between the heat dissipation device 16 and housing 12 to avoid the heat of the heat dissipation device 16 transmitting to the housing 12.
However, the optical engine 10 in FIG. 1 still has following problems.
1. Part of the dumped light beam 113 is reflected or scattered by the inner wall of the heat dissipation device 16 to the projection lens 14 or the inner wall of the housing 12. Meanwhile, the part of the dumped light beam 113, which is projected to the projection lens 14, affects the normal image and reduces the contrast; another part of dumped light beam 113, which is projected into the inner wall of the housing 12, raises the temperature of the whole optical engine 10.
2. Due to the airtight state of the housing 12, when the dumped light beam 113 is absorbed by the heat dissipation device 16, the temperature of the heat dissipation device 16 is higher than that of the DMD 13 and the projection lens 14, which causes heat convection. At this time, the heat is circulated inside the housing 12 to heat up the DMD 13 and the projection lens 14. At the same time, the DMD 13 and the projection lens 14 are heated by radiation. Thus, part of the heat from the dumped light beam 113 accumulates in the housing 12 to make the DMD 13 and the projection lens 14 aged, which further affects the reliability and the service life of the optical engine 10.
There are two embodiments of the optical engine with the heat dissipation design in the Taiwan patent I281091, as shown in FIGS. 2A and 2B.
Referring to FIG. 2A, its embodiment is similar to FIG. 1. An optical engine 20 includes a light source system 21, a housing 22, a DMD 23, a projection lens 24, a first heat dissipation device 25 and a heat insulation device 26.
The light source system 21 provides an incident light beam 211 to the DMD 23. The DMD 23 receives the incident light beam 211 from the light source system 21, modulates and reflects the incident light beam 211 to form an image light beam 212 (ON light) or a dumped light beam 213 (OFF light). The image light beam 212 is transmitted to the projection lens 24 and projected to an outer screen to form an image, while the dumped light beam 213 is absorbed by the first heat dissipation device 25, which insulates the heat conduction with the housing 22 via the heat insulation device 26. Furthermore, the embodiment has a second heat dissipation device 27 disposed at the back of the DMD 23 to absorb the heat of the DMD 23.
Referring to the embodiment of the FIG. 2B, the dumped light beam 213 goes through a light transparent board 28 to project to a light shade device 29. The disadvantage of this design is that the surfaces of the light transparent board 28 and the light shade device 29 still reflect (scatter) part of the dumped light beam 213 back into the housing 22.
Due to the disadvantages in above mentioned conventional technology, it is necessary to raise an effective solution.